https://www.youtube.com/watch?v=Qqsf_UJcfBc https://www.youtube.com/watch?v=Qqsf_UJcfBc

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Note the kinks in the phospholipid tails.

Recall this is due to double bonds (unsaturated) and Recall this is due to double bonds (unsaturated) and

increases fluidity

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Note the cell membrane is a bilayre, due to Note the cell membrane is a bilayre, due to

spontaneous positioning of the polar and non-polar spontaneous positioning of the polar and non-polar

ends of the phospholipids which form it.

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

Note structural support of the protein filaments acting like scaffolding – Note structural support of the protein filaments acting like scaffolding – giving the cell a shape

giving the cell a shape

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Note also the cholesterol studded here and there on either side of the Note also the cholesterol studded here and there on either side of the bilayre; it maintains fluidity, preventing the cell from ‘melting’ in heat and bilayre; it maintains fluidity, preventing the cell from ‘melting’ in heat and

from becoming too rigid in the cold from becoming too rigid in the cold



https://www.youtube.com/watch?v=CNbZDcibegY https://www.youtube.com/watch?v=CNbZDcibegY

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In the freeze fracture technique cells are flash frozen in liquid nitrogen, In the freeze fracture technique cells are flash frozen in liquid nitrogen, dropped from a height, or split with a knife, and gold is evaporated onto dropped from a height, or split with a knife, and gold is evaporated onto their exposed surfaces; with the hope that something interesting might their exposed surfaces; with the hope that something interesting might be visualized on the screen of the scanning electron microscope

be visualized on the screen of the scanning electron microscope

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How does a SEM work?

The SEM is an instrument that The SEM is an instrument that

produces a largely magnified image produces a largely magnified image by using electrons instead of light to by using electrons instead of light to form an image. A beam of electrons form an image. A beam of electrons is produced at the top of the

is produced at the top of the

microscope by an electron gun. The microscope by an electron gun. The electron beam follows a vertical path electron beam follows a vertical path through the microscope, which is through the microscope, which is held within a vacuum. The beam held within a vacuum. The beam travels through electromagnetic travels through electromagnetic fields and lenses, which focus the fields and lenses, which focus the beam down toward the sample. Once beam down toward the sample. Once the beam hits the sample, electrons the beam hits the sample, electrons and X-rays are ejected from the

and X-rays are ejected from the sample.

sample.

Detectors collect these X-rays, Detectors collect these X-rays, backscattered electrons, and backscattered electrons, and

secondary electrons and convert secondary electrons and convert them into a signal that is sent to a them into a signal that is sent to a screen similar to a television screen.

screen similar to a television screen.

This produces the final image.

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FUNCTIONS OF THE CELL MEMBRANE FUNCTIONS OF THE CELL MEMBRANE

PROTEINS PROTEINS

Some form "channels" through which Some form "channels" through which various substances enter and depart from various substances enter and depart from the cell. Enzymes help speed up chemical the cell. Enzymes help speed up chemical reactions. Some proteins, when attached to reactions. Some proteins, when attached to

special chemicals, serve as receptors, special chemicals, serve as receptors, setting functions such as hormone synthesis setting functions such as hormone synthesis

into operation. This attachment launches into operation. This attachment launches the beginning of a certain function such as the beginning of a certain function such as the synthesis of hormone in the cell. The the synthesis of hormone in the cell. The

identifiers of the cell are the proteins identifiers of the cell are the proteins receiving information regarding whether receiving information regarding whether other cells in the body are foreign invaders.

other cells in the body are foreign invaders.

Some proteins assume structural functions;

others serve as attachment points for cells others serve as attachment points for cells to adhere to one another. Other proteins are to adhere to one another. Other proteins are

important in anchoring the cell skeleton.

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 Cell-cell recognition is critically important for any kind of organism Cell-cell recognition is critically important for any kind of organism to function. This job is mainly undertaken by membrane

to function. This job is mainly undertaken by membrane

carbohydrates. In order for cells to recognize each other, they bind carbohydrates. In order for cells to recognize each other, they bind to molecules found on the cell’s surface, which happen to mostly to molecules found on the cell’s surface, which happen to mostly be carbohydrates. Membrane carbohydrates sometimes bind be carbohydrates. Membrane carbohydrates sometimes bind

covalently to lipids, forming what is to be called a glycolipid, while covalently to lipids, forming what is to be called a glycolipid, while the majority of membrane carbohydrates are covalently bound to the majority of membrane carbohydrates are covalently bound to proteins, making the two together glycoproteins. Carbohydrate proteins, making the two together glycoproteins. Carbohydrate markers found on red blood cells, for example, dictate what blood markers found on red blood cells, for example, dictate what blood type you are.

type you are.

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Passive transport: diffusion

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Net Diffusion to Equilibrium

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Only small and hydrophobic molecules can diffuse Only small and hydrophobic molecules can diffuse

through the cell membrane!

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Recap = Facilitated diffusion is when an assisting protein Recap = Facilitated diffusion is when an assisting protein

remains in place and “helps” a molecule across by remains in place and “helps” a molecule across by

undergoing a change in shape that moves the binding site undergoing a change in shape that moves the binding site

from one side of the membrane to the other. It is still from one side of the membrane to the other. It is still passive since the molecule is still moving down their passive since the molecule is still moving down their

concentration gradient.

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Passive transport:

Osmosis = the movement of water through a semi- Osmosis = the movement of water through a semi-

permeable membrane from high to low permeable membrane from high to low

concentration

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Tonicity Tonicity

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Tonicity II

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Active transport:

Active transport: endocytosis and endocytosis and exocytosis

exocytosis



Endocytosis is used by cells to move water based Endocytosis is used by cells to move water based

solutions, macro molecules, or larger objects, such as solutions, macro molecules, or larger objects, such as

cell fragments or even whole cells, from outside a cell to cell fragments or even whole cells, from outside a cell to

the inside of the cell. Exocytosis is the reverse of the inside of the cell. Exocytosis is the reverse of

endocytosis, that is, the

endocytosis, that is, the movement movement of materials from the of materials from the inside to the outside of the cell. Both

inside to the outside of the cell. Both types of types of transport transport move the materials using membrane-bound vesicles.

move the materials using membrane-bound vesicles.

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Three types of endocytosis Three types of endocytosis

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Phagocytosis Phagocytosis (transport of actual particles), (transport of actual particles), pinocytosis pinocytosis (transport of water, along with any solutes in

(transport of water, along with any solutes in the water the water ), ), and and receptor-mediated endocytosis receptor-mediated endocytosis

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In receptor-mediated endocytosis, specific macro molecules outside In receptor-mediated endocytosis, specific macro molecules outside the cell attach to the binding sites of receptor proteins, even if they are the cell attach to the binding sites of receptor proteins, even if they are in low concentrations ex transferrin – the source of blood iron and LDL in low concentrations ex transferrin – the source of blood iron and LDL

- for membrane cholesterol. These receptors are embedded in the - for membrane cholesterol. These receptors are embedded in the

plasma membrane in specialized regions called coated pits.

After the contents of the vesicle are released inside the cell, the After the contents of the vesicle are released inside the cell, the

receptor

proteins are reused to form new coated pits.

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Crash Course Recap: Crash Course Recap:

https://www.youtube.com/watch?v=dPKvHrD1eS4

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Summary:

 1. Endocytosis brings molecules into a cell while 1. Endocytosis brings molecules into a cell while exocytosis takes molecules out of a cell.

exocytosis takes molecules out of a cell.

 2. Both processes use vesicles for molecular 2. Both processes use vesicles for molecular transport.

transport.

 3. Endocytosis creates vesicles while exocytosis 3. Endocytosis creates vesicles while exocytosis can destroy them.

can destroy them.

 4. The primary function of endocytosis is getting 4. The primary function of endocytosis is getting nutrients and the primary function of exocytosis is nutrients and the primary function of exocytosis is

expelling waste.

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Active Transport Active Transport

Certain molecules need to be kept in the cell at a concentration that is Certain molecules need to be kept in the cell at a concentration that is

greater than the surrounding environment.

This requires the expenditure of energy, usually in the form of ATP This requires the expenditure of energy, usually in the form of ATP

 https://www.youtube.com/watch?v=_bPFKDdWlCghttps://www.youtube.com/watch?v=_bPFKDdWlCg

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